Due to a shortage of some lines, a number of online retailers are selling Lego products for over double the recommended price.
Argos and Asda told Sky News Online that the Star Wars and Indiana Jones sets have been the best sellers over the festive period and are now listed as out of stock on both firms' websites.
Tesco said it has seen a large rise in demand but that it is expecting more deliveries this week.
The popular Star Wars Darth Vader's Tie Fighter is listed as £29.87 by Asda but is being sold on Amazon for £54.99. The Power Miner's Claw Digger is priced at £14.67 but is selling on Amazon for £29.75.
Amazon told Sky News Online that these products are only available through third-party sellers who are free to set their own prices.
Melissa Wallace from Lego said it was "unfortunate that people choose to exploit commercial opportunities" but that Lego sets fixed prices and has nothing to do with web sales.
She added that the company has had a record-breaking year with sales up by 30 per cent, the best figures since Lego began in the UK in 1959.
She reassured customers that there were only pockets of stock that children would not be able to get this Christmas but that most sets would be available for last minute gifts.